If I had to guess most classes operate on a formula that outputs a nice little curve which probably involves a lot of mathing than just those two points of variance (overal variance, standard dev, mean, etc).
Those crit values vs normal values are on that curve that balances the overall damage BRD does. More points needed on graph maybe.
BRD doesn't do the best damage so it'd make sense that when it does crit, its crit are big brain to bandaid the sad feels.
It's very late and I am half asleep. Forgive me.